Fusing apparatus

ABSTRACT

A fusing apparatus is provided for heat fusing a toner image to a sheet of final support material. The apparatus includes curl reducing means comprising at least one seal adjacent the fusing zone for limiting air flow at the zone to an amount at which curl of the sheet is substantially reduced. At least one of the seals comprises an elongated brush-like member.

United States Patent 11 1 Lynch [111 3,849,907 [451 Nov. 26, 1974 FUSINGAPPARATUS [75] Inventor: Thomas Lynch, Fairport, NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

22 Filed: Dec. 4, 1973 21 Appl. No.: 421,709

[52] US. Cl. 34/242, 34/155 [51] Int. Cl. F26b 25/00, F2619 13/04 [58]Field of Search 432/59-60,

432/227-228, 115, 242, 244; 219/216, 388, 469, 343; 34/242, 155; 68/5 E;277/DIG. 7

[56] References Cited UNITED STATES PATENTS 3,040,702 6/1962 Eng et al68/5 E 3,071,866 1/1963 Mangus 34/242 5/1963 Morrison 34/242 3,207,1299/1965 Limberger 219/216 3,291,468 12/1966 Albertsen et aL. 432/2423,505,497 4/1970 Lawes et a1 219/216 Primary ExaminerJohn J. CambyAssistant Examiner-Henry C. Yuen Attorney, Agent, or Firm-PaulWeinstein; Clarence A. Green; James J. Ralabate 57 ABSTRACT A fusingapparatus is provided for heat fusing a toner image to a sheet of finalsupport material. The apparatus includes curl reducing means comprisingat least one seal adjacent the fusing zone for limiting air flow at thezone to an amount at which curl of the sheet is substantially reduced.At least one of the seals comprises an elongated brush-like member.

11 Claims, 4 Drawing Figures FUSING APPARATUS BACKGROUND OF THEINVENTION This invention relates to a fusing apparatus for heat fusing atoner image to a sheet of final support material including means forreducing curl of the sheet during fusing.

When a sheet of final support material having a toner image on a sidethereof is subjected to fusing by means of a radiant heat fuser some ofthe moisture in the sheet is driven out. Depending on the quantity ofmoisture driven out changes in the length and width of the sheet occuras well as a severe curl. Curl in the resulting sheet after fusing is asevere problem for a reproducing ma chine, particularly those of thexerographic type. The tendency of the sheet to curl during fusing is oneof the causes of jams in the region of the fuser. Curl is also asignificant problem in reproducing machines adapted to provide images onboth sides of the sheet, a process referred to in the art as duplexing.A duplexing apparatus requires that the sheet be refed through the machine. Sheets with a severe curl are extremely difficult and sometimesimpossible to feed without persistent jamming problems along the paperpath.

The problem of sheet curl due to radiant heat fusing has been recognizedin the art as exemplified by US. Pat. Nos. 2,807,703 and 2,807,704. Inthese patents the fusing apparatus is designed to selectively heat thetoner image on the sheet to its fusing point while leaving the sheet perse at a temperature sufficiently below the fusing point of the toner toavoid curl. In fact, the temperature of the sheet is maintained belowthe boiling point of water so that a substantial portion of the originalmoisture content of the sheet is not removed. The apparatuses describedin these patents are particularly applicable to record cards. In thefirst of these patents, three embodiments of the fusing apparatus forcarrying out the invention are described. In each apparatus the transferof heat energy to the record card by conduction and convection is keptnegligible by a suitable means, and thereby, since the record card perse is made from paper stock and does not readily absorb radiant energy,the temperature of the record card is kept at a lower value than theboiling point of water. Transfer of heat energy by conduction andconvection is reduced either by heat extraction or so called fixingstation cooling, or by the use of a heat transfer barrier for preventingheat transfer by conduction and convec tion such as a water filled glassjacket, or in accordance with the third embodiment, by focusing andconcentrating the radiant energy on the toner image.

While the approaches of these patents may operate satisfactorily forfusing toner images on record cards, this would not necessarily followfor fusing toner images on support sheet of other types. Toner images onrecord cards are generally'not very dense and, therefore, comprise verylittle toner so that not as much heat energy is required to fuse them.Conventional copying machines can provide denser toner images containingconsiderably greater proportions of toner over the sheet surface, whichwould require a greater quantity of heat energy to fuse them to thesheet. Therefore, it is possible that the apparatuses of the aforenotedpatents would not operate satisfactorily in the environment of a copyingmachine since by maintaining the temperature of the sheet below theboiling point of water insufficient heat energy would be impressed onthe toner image to consistently fuse the toner image to the sheet.

One successful solution to this problem is set forth in copending US.application Ser. No. 421,710, filed of even date herewith (AttorneysDocket No. D/73702). In that case a curl reducing means is provided in afusing apparatus which comprises at least one seal adjacent to thefusing zone which limits the air flow at the zone to an amount at whichcurl of the sheet is reduced or eliminated. The seals preferablycomprise strip-like members of a polymeric material.

The seals of the copending application should be resilient and heatresistant. Teflon and Mylar are disclosed as usable materials. Whilethese materials perform their function adequately, their useful life inthe machine environment is not as great as desired because of theeffects of their elevated temperature environment, though they have beenused commercially. It has been found that Mylar is not as heat resistantdesired. Teflon, while being heat resistant, is unable to maintain itsresiliency in this environment. The elevated temperatures eventuallycause the Teflon to take a permanent set in a deflected conditionthereby reducing its biasing ability.

One solution which was proposed to overcome the abovenoted problems wasto employ a polymeric foam, specifically polyurethane foam as the seal.This approach was not successful since the seal which was interposedbetween a transport roll and the fuser caused sufficient drag tointerfere. with the uniform rotation of the roll.

. SUMMARY OF THE INVENTION In accordance with this invention a fusingapparatus has been developed wherein curl of the sheet during fusing issubstantially reduced or eliminated. The fuser includes a source of heatradiation. A fusing zone is defined wherein the heat source is effectiveto fuse a toner image to a sheet of final support material. A flow ofair is present at the zone due to influences which are internal and/orexternal of the fuser. Curl reducing means are provided which compriseat least one seal adjacent to the fusing zone which limits the air flowat the zone to an amount at which curl of the sheet is re duced oreliminated. In accordance with this invention the seal comprises anelongated brush'like member.

Contrary to the aforenoted prior art teachings in accordance with thisinvention, the air flow has to be limited severely in order to reducemoisture gradients and to prevent the moisture driven off from the sheetfrom being completely withdrawn from the fusing zone.

In accordance with preferred embodiments, transport means are providedat the exit and/or entrance regions of the fuser to transport the sheet.One or more of these transports may include suction means for holdingthe sheet to the transport. The seals preferably extend between thetransports and the fuser. Preferably the seal comprises an elongatedbacking strip and a plurality of elongated fibers extending out from thestrip in a brush-like configuration.

Therefore, it is an object of this invention to provide an improvedfusing apparatus for heat fusing a toner image to a sheet of finalsupport material.

It is a further object of this invention to provide an apparatus asabove including improved means for re ducing the curl of the sheetduring fusing.

It is a still further object of this invention to provide an apparatusas above wherein the curl reducing means includes a brush-like seal.

These and other objects will become more apparent from the followingdescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows schematically anexemplary reproducing machine including the fusing apparatus of thisinvention.

FIG. 2 is a perspective view of a sheet of final support material afterfusing by a prior art radiant fuser.

FIG. 3 is a cross-sectional side view of the fusing apparatus of thisinvention including the curl reducing means.

FIG. 4 is a perspective view of a brush-like seal in accordance withthis invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG.1 in accordance with this invention, a fusing apparatus 1 is providedfor heat fusing a toner image to a sheet 2 of final support material.The fusing apparatus 1 includes a fuser 3 having a source of heatradiation 4 for application to the sheet. The fuser 3 defines a fusingzone 5 wherein the heat source 4 is effective to fuse the image to thesheet 2. A flow of air is present at the zone 5 due to influences whichmay be internal and/or external of the fuser 3. An essential part ofthis invention comprises means which cooperate with the fuser 3 forreducing curl of the sheet 2 during fusing. The curl reducing means 6preferably comprise at least one seal comprising a brush-like memberadjacent to the fusing zone 5 which is adapted to limit air flow throughthe zone to a volume at which curl of the sheet is substantiallyreduced.

It is believed in accordance with this invention that paper curl in thefinal support sheet after fusing by means of a radiant fuser is theresult of plastic deformation of the paper sheet. The deformation ismade up of two components which may be summed algebraically. Onecomponent is related to the type of paper and to the bulk paper changesthat occur during fusing. It is possible to think of these as resultingfrom one or both of the following: (1) a locked in asymmetric residualstress distribution which relaxes or yields under a bulk temperature ormoisture level excursion. (2) variations in paper properties across thethickness of the sheet, as for example, the coefficient or expansionwith moisture. This can result in non-uniform elongation of the sheetand curl in the absence of any assymctry or gradients. The othercomponent is believed to relate to the asymmetrical conditions orgradients imposed on the paper by the fuser and adjacent machinecomponents or other external influences. The curl from this component isalways in the direction of the source of radiant energy.

The curl is believed to result from stresses imposed on the sheetassociated with the gradient moisture through the thickness of thesheet. This invention is not directed at preventing curl induced bymechanical deformation which may occur in the copier and which can, infact, result in curl in either direction depending on the direction ofdeformation. For example, curl induced by a roll fusing apparatus.

The primary source of the stresses is the moisture gradient which causesthe top surface of the sheet to ploys an image recording drum-likemember 11 the outer periphery of which is coated with a suitablephoshrink more than the bottom surface. The moisture gradient isdetermined by the temperature gradient, the initial moisture content andthe moisture mass transfer effects; In many cases the moisture masstransfer is significant. In configurations where the fuser is near anair moving device such as a suction box ofa vacuum transport the airmoving device may aggrevate curl by increasing the rate of moisture masstransfer due to increased air flow in the fusing zone. The rate ofmoisture mass transfer is substantially increased in the top surface ofthe sheet thus causing a larger moisture gradient which results inhigher stresses ands greater deformation of the sheet. Other aspects ofthe mechanism causing curl in the sheets are described in US. Pat. No.2,807,703.

The aforenoted description of the mechanism for causing curl is notmeant to be limitative of the invention and is presented here by way ofexample. The aforenoted mechanism is believed to be the mechanisminvolved in accordance with this invention. however. other factors notyet appreciated could be taking part in the mechanism.

Referring now to FIG. 2, a sheet 2 of final support material is shownafter fusing by an apparatus not including the curl preventing means 6in accordance with this invention. The sheet 2 shown therein has asubstantial curl 7 of about 1.5 inches at the trailing edge portion 8thereof. This type of curl 7 in a sheet 2 is formed by an apparatus 10as will be described in more detail with reference to FIG. 1 when thecurl preventing means 6 are not employed. In other apparatuses the curl7 may be more or less pronounced. There may be curl 7 at the trailing 8and/or the leading 9 edges of the sheet 2. Irrespectively, by followingthe teachings of the present invention, it should be possible tosubstantially reduce or eliminate curl 7 from the sheet 2 due to fusingwhen the curl is produced by means other than mechanical deformation.

Referring now to FIG. 1, there is shown by way of example an automaticxerographic reproducing machine l0 which incorporates the improvedfusing apparatus 1 of the present invention. The reproducing machine 10depicted in FIG. 1 illustrates the various components utilized thereinfor producing copies from an original. Although the fusing apparatus 1of the present invention is particularly well adapted for use in anautomatic xerographic reproducing machine 10, it should become evidentfrom the following description that it is equally well suited for use ina wide variety of machines where an image is fused to a sheet of finalsupport material and it is not necessarily limited in its application tothe particular embodiment shown herein.

The reproducing machine 10 illustrated in FIG. 1 emtoconductive material12. One type of suitable photoconductive material is disclosed in US.Pat. No. 2,970,906 issued to Bixby in 1961. The drum 11 is suitablyjournaled for rotation within a machine frame (not shown) by means of ashaft 13 and rotates in the direction indicated by arrow 13, to bringthe image retaining surface thereon past a plurality of xerographicprocessing stations. Suitable drive means (not shown) are provided topower and coordinate the motion of the various cooperating machinecomponents whereby a faithful reproduction of the original input sceneinformation is recorded upon a sheet 2 of final support material.

The practice of xerography is well known in the art and is the subjectof numerous patents and texts including Electrophotography by Schaffert,published in 1965, and Xerography and Related Processes by Dessauer andClark, published in 1965. The various processing stations for producinga copy of an original are herein represented in FIG. 1 as blocks A to E.Initially, the drum 11 moves photoconductive surface 12 through chargingstation A. At charging station A an electrostatic charge is placeduniformly over the photoconductive surface 12 of the drum ll preparatoryto imaging. The charging may be provided by a corona generating deviceof a type described in U.S. Pat. No. 2,836,725 issued to Vyverberg in1958.

Thereafter, the drum 11 is rotated to exposure station B where thecharged photoconductive surface 12 is exposed to a light image of theoriginal input scene information, wherby the charge is selectivelydissipated in the light exposed regions to record the original inputscene in the form of a latent electrostatic image. A suitable exposuresystem may be of the type described in U.S. Pat. application, Ser. No.259,181 filed June 2, 1972.

After exposure, drum 11 rotates the electrostatic latent image recordedon the photoconductive surface 12 to development station C wherein aconventional developer mix is applied to the photoconductive surface 12rendering the latent image visible. A suitable development station isdisclosed in U.S. Pat. application, Ser. No. 199,481 filed Nov. 17,1971. The application describes a magnetic brush development systemutilizing a magnetizable developer mix having carrier granules and atoner colorant. The developer mix is continuously brought through adirectional flux field to form a brush thereof. The electrostatic latentimage recorded on photoconductive surface 12 is developed by bringingthe brush of developer mix into contact therewith.

The developed image on the photoconductive surface 12 is then broughtinto contact with a sheet 2 of final support material within a transferstation D and the toner image istransferred from the photoconductivesurface 12 to the contacting side of the final support sheet 2. Thefinal support material may be paper, plastic, etc., as desired. Afterthe toner image has been transferred to the sheet of final supportmaterial 2, the sheet with the image thereon is advanced to a suitablefuser 3, which coalesces the transferred powdered image thereto. Onetype of suitable fuser is described in U.S. Pat. No. 2,701,765, issuedto Codichini, et al, in 1955. After the fusing process, the sheet 2 isadvanced by snuffing rolls 14 and then by rolls 15 to a catch tray 16for subsequent removal therefrom by the machine operator.

Although a preponderance of the toner powder is transferred to the finalsupport material 2, invariably some residual toner remains on thephotoconductive surface 12 after the transfer of the toner powder imageto the final support material 2. The residual toner parti cles remainingon the photoconductive surface 12 after the transfer operation areremoved therefrom as it moves through cleaning station E. Here theresidual toner particles are first brought under the influence of acleaning corona generating device (not shown) adapted to neutralize theelectrostatic charge remaining on the toner particles. The neutralizedtoner particles are then mechanically cleaned from the photoconductivesurface 12 by conventional means as, for example, the use of aresiliently biased knife blade as set forth in U.S. Pat. No. 3,660,863issued to Gerbasi in 1972.

If desired, in accordance with this invention, the sheets 2 of finalsupport material processed in the automatic xerographic reproducingmachine 10 can be stored in the machine within a removable papercassette 17. A suitable paper cassette is set forth in U.S. Pat.application, Ser. No. 208,138 filed Dec. 15, 1971, now U.S. Pat. No.3,767,187.

The reproducing apparatus in accordance with this invention can alsohave the capability of accepting and processing copy sheets 2 of varyinglengths. The length of the copy sheet 2, of course, being dictated bythe size of the original input scene or information recorded on thephotoconductive surface 12. To this end the paper cassette 17 ispreferably provided with an adjustable feature whereby sheets of varyinglength and width can be conveniently accommodated. In operation theeassette 17 is filled with a stack of final support material 2 ofpre-selected size and the cassette is inserted into the machine bysliding along a base plate (not shown) which guides the cassette intooperable relationship with a pair of feed rollers 18. When properlypositioned in communication with the feed. rollers 18, the top sheet ofthe stack is separated and forwarded from the stack into the transferstation D by means of registration rolls 19.

It is believed that the foregoing description is sufficient for purposesof the present application to illustrate the general operation of theautomatic xerographic reproducing machine 1 which can embody theteachings of the present invention.

Referring now to FIG. 3, that portion of the reproducing machine 10 ofFIG. 1 embodying the fusing apparatus l of this invention is shown ingreater detail. The view shown is a side view and it should be readilyevident that the fusing apparatus extends across the entire sheet in adirection normal to the plane of the Figure. The image bearing sheet 2,after passing through the transfer station D of FIG. 1 upon separationfrom the photoconductive surface 12, is allowed to fall into contactwith a vacuum belt transport system 20 which conveys the sheet directlyto the fusing apparatus 1.

The fusing apparatus 1 shown includes a radiant type fuser 3. The fuser3 includes a heated platen 30 mounted to engage the non-image bearingside of the copy sheet 2 which moves in sliding contact therewith as itis transported through the fusing zone. The heated platen 30 is designedso that an efficient heat flow is established between the platen and thecopy sheet 2 to raise the temperature of the sheet rapidly to a levelsomewhat below the sheets scorch temperature. By controlling thetemperature of the sheet 2 in this manner the ability of the sheet toact as a heat sink during image fixing is minimized. The radiant energysource for fusing is provided by an infrared quartz lamp 31 which ismounted in a reflector assembly 32 in opposing relationship to theheated platen 30 and in a position to thermally communicate with thenewly imaged side of the copy sheet 2. Preferably the spectral output ofthe lamp 31 is within a range at which the imaging material which may betoner for a xerographic machine 10 is highly absorptive and at which thesupport mate rial 2 which may be paper is relatively non-absorptive. Asa result, the toner images are rapidly raised to the desired fusingtemperature while the support sheet 2 remains at a relatively lowertemperature. A forced air cooling chamber 33 is provided about thebackside of the reflector assembly 32 to cool the fuser 3 in operatlon.

A heating element 34 is provided in the platen to maintain it at thedesired temperature during standby periods. When the quartz lamp 31 isoperated the preheat element is disconnected and the platen 30 receivesits heat input directly from the quartz lamp.

The leading edge of the sheet 2 bearing the image is pushed through theentrance port 35 to the fusing zone 5 and moves in sliding contact overthe platen 30 through the fuser exit port 36 into a pair of cooperatingtransport rolls and 41 which comprise a flame snuffing apparatus. Thelower snuffing roll 41 is positioned such that its outer periphery liesbelow the plane of the fuser platen 30 whereby in operation the snuffingrolls 40 and 41 are operative to hold the sheet 2 in sliding contactwith the fuser platen 30. The sheet is also held in contact with theplaten 30 by means of suction communicated via suction chamber 37 andplaten suction ports 38.

The snuffing rolls 40 and 41 forward the sheet along a guide plate 42into the nip of a pair of advancing rolls 43 which deposit the sheetwithin a collecting tray 16. The collecting tray 16 includes a baseplate 44 inclined upwards and an upwardly turned margin stop 45.

The advancing rolls 43 serve to drive the sheet 2 into the collectingtray 16. The advancing rolls 43 further include a compact propellingmechanism 46 which moves the sheet 2 rapidly and efficiently intoalignment against the stop 45. The propelling mechanism is described ingreater detail in US. application, Ser. No. 317,028 filed Dec. 20, 1972.

Having thus described the operation of the fusing apparatus 1, furtherreference will now be given to the curl control means 6 in accordancewith this invention.

In the embodiment of FIG. 3 the transport 20 comprises a vacuumtransport having a suction means 21 which draws air in through orbetween the belts 22. The suction means is connected to any conventionalsource of suction (not shown). The suction means 21 cooperates with thebelts 22 to firmly hold a sheet 2 of final support material in contactwith the transport. The suction means 21 comprises, however, only one ofmany possible external influences in the machine 10 which can cause anair flow through the fusing zone 5. The suction means 21 draws air infrom an external port (not shown). Air flows through various passagewaysdefined by the machine components and sub-stations. The paper pathprovides one of the key flow channels for the air which flows to thesuction means 21. [n the absence of the curl preventing means 6 inaccordance with this invention air is drawn through the fuser 3 in orderto satisfy the requirements of the suction means 21 as shown by thearrows 50. While this flow of air has a beneficial effect with respectto cooling the sheet 2 prior to its being received by the snuffing rolls40 and 41, it has deleterious effect in that it results in a substantialcurl being formed in the sheet during fusing.

There is also in the fuser 3 shown an internal means which causes a flowof air through the fusing zone 5. The internal means comprises a seriesof orifices 38 in the platen 30 which communicate with a suction meanscomprising the chamber 37. The purpose of these orifices 38 is toprovide a vacuum holddown for holding the sheet 2 in contact with theplaten 30 as it passes through the fuser 3. When the sheet does notcover these orifices a substantial air flow is produced. The directionof this air flow will vary depending on whether the sheet is entering orleaving the fuser. Another internal cause of air flow comprises theconductive air currents associated with the fuser.

Therefore, as shown, an air flow through the fusing zone is created bothby external influences and by internal influences. It is believed,however, that either of these influences alone would be sufficient toprovide an air flow.

In accordance with this invention it is desired to reduce the flow ofair through the fuser so as to reduce the curl producing effects of themoisture gradients induced in the sheet 2 during fusing, The mechanismby which this is accomplished is not fully understood, but it isbelieved to be the result of a localized condition in the fusing zonewhich reduces the rate that the moisture is driven out of the sheetduring the period the thermal and moisture gradients are caused in thesheet by fusing. This may, for example, be due to a localized increasedvapor pressure condition which can form due to the restricted air flowand which temporarily prevents or reduces the rate at which moisture canexit from the sheet 2 until the thermal and moisture gradients in thesheet have been reduced or eliminated.

The temperature and moisture gradients in the por tion of the sheet 2being heated occur for an extremely short period of time, a matter offractions of a second. Therefore, if the sheet can be sufficientlyrestrained during this period or if the rate of moisture evaporated fromthe sheet during the period can be reduced, curl 7 can be reduced.

In the apparatus 1 shown, without the curl preventing means 6 the sheetsare subject to substantial trail edge curl 7 as shown in FIG. 2. Leadedge 9 curl is not pronounced because of the inneraction of the vacuumtransport 20 with the sheet 2. It is believed that the vacuum transport20 prevents the sheet 2 from being deformed by the influence of themoisture gradients by restraining deformation of the sheet. However,after the sheet 2 leaves the vacuum transport 20 the trail edge 8 of thesheet is not sufficiently restrained and, therefore, is subject tosubstantial curl as, for example, that shown in FIG. 2.

When the lead edge 9 of the sheet 2 enters the fusing zone 5 theremainder of the sheet closes off some of the suction ports (not shown)in the top of the vacuum transport 20 thus reducing the flow of air flowthrough the fusing zone 5. As the sheet 2 progresses through the zone 5more of the suction ports, particularly those adjacent to the fuser 3,are uncovered by the sheet 2 thereby increasing the air flow through thezone. This is also believed to be a major factor in causing thepronounced trail edge 8 curl and insignificant lead edge 9 curl usingthe specific apparatus 1 shown.

Therefore, in accordance with this invention curl preventing means 6 areprovided which comprise in the embodiment shown one or more seals 61,62, 63 and 64 adjacent to the fusing zone 5 which are adapted to limitthe air flow at the zone to an amount at which curl of the sheet issubstantially reduced or eliminated. In the apparatus 1 shown whichincludes the external influence of the vacuum transport 20, theprovision of the seal 61 between the top portion 65 of the fuser 3 andthe upper transport roll 40 at the exit side of the fuser provides asubstantial reduction in curl as com pared to the same apparatus withoutthe seal 61. Experimentally, the reduction in curl due to this seal 61has been shown to be as much as about 60 percent or more. Furtherreductions in curl can be achieved by providing additional seals 62, 63and 64 as, for example, the lower seal 62 between the bottom portion 66of the fuser 3 and the lower transport roll 41 has been determined toprovide a further 5 to l0 percent or more improvement in curl reduction.At the upstream side of the fuser 3, because of the external influenceof the vacuum transport 20, it has been found desirable to provide slotsor holes 67 in the seal 63 between the fuser and the cleaning station E.This allows air flow from the channel 68 as shown by arrow 69 to flow tothe transport and thereby reduces the amount of flow drawn through thefuser. The provision of holes 67 in this particular seal 63 which alsoserves to guide the sheet provides a further percent or more improvementin curl 7 reduction. Finally, a seal 64 between the vacuum transport andthe lower portion 66 of the fuser 3 provides some improvement, but notthat significant, namely, less than 5 percent.

It is quite apparent that the fusing apparatus illus trated in FIG. 3requires seals between the downstream sheet transport 40 and 41 and thefusing apparatus 3 in order to substantially reduce or eliminate curl 7.It should also be apparent that had the vacuum transport 20 or otherexternal source of substantial air flow through the fuser 3 beendownstream of the fuser rather than upstream thereof then the effectiveseals for reducing air flow through the fuser would have been theupstream seals 63 and 64, rather than the downstream seals 61 and 62. Inthis case the seal 63 between the upper portion 65 of the fuser 3 andthe adjacent housing E would have had to be impervious, whereas theseals 61 and 62 on the downstream side of the fuser could have beenpervious as desired.

In the embodiment shown the internal suction means 37 and 38 does notexert a controlling influence on the amount of curl which is formed.Regulation of the suction force here, in cooperation with the seals 6164 could help reduce air flow through the fusing zone 5. Converselyincreasing the suction force would restrain deformation caused by themoisture gradient, however, it would also increase the retardationforces on the sheet 2 which could cause the sheet to stall in the fuser3 which is undesirable.

The location of the seals 61 64 has to be determined based on the airfiow conditions in the apparatus in which the fuser 3 is employed andseals 61 64 may be employed at one or all of the locations shown inorder to provide the reduced air flow through the fuser. The mostsignficiant seals will be those adjacent the image containing side ofthe sheet 2, for an apparatus 10 where the sheet is passed over a platen30, since it is on this side of the sheet that the greatest air flowoccurs.

It is an essential aspect of this invention that at least one of theseals 61 64 comprises an elongated member having a brush-likeconfiguration. The seals 61-64 are at least coextensive with the fusingzone in the transverse direction, (e.g., the direction normal to theplane of FIG. 3). Referring to FIG. 4, a seal 100 in accordance withthis invention is shown. The seal comprises a backing strip 101 having aplurality of elongated fibers 102 extending out therefrom in abrush-like configuration. The fibers 102 may comprise individual fibersor tufts of fibers formed, for example, from a pile of yarn. The densityof the fibers should be such as to provide a substantial baffle or sealto the flow of air through the seal. Preferably it should prevent airflow through the channel being sealed.

The backing strip 101 preferably comprises a composite comprising ametal backing component 103 and a polymeric support component 104,preferably nylon, adjacent to the brush fibers 102. The brush fibers 102are woven into the nylon support 104 and the metal component 103 iscrimped over the support to provide added mechanical strength. Whilenylon appears to be the preferred material for use as the fibers 102 inthe brush-type seals of this invention, other heat resistant materialscould also be employed if desired, particularly other polymericmaterials. The brush-type seals may be secured to the fuser by anyconventional means as, for example, the use of screws (not shown).

In the apparatus of FIG. 3, the upper roll 40 is an idler roll and whenthe seal 100 is interposed between an idler roll 40 and the fuser 3, it.is necessary to avoid too dense a brush or else a drag is placed on theidler roll which prevents its uniform rotation.

By using a brush configuration instead of a strip-type member the lifeof the seals 61 64 can be substantially extended. The brush-type seal100 does not require the same degree of resiliency for the: fibers 102as is required for the material of the strip-type seals. Further, theresiliency of the individual fibers 102 is maintained by the addedsupport they receive from adjacent fibers.

In the apparatus shown a plurality of spaced apart circumferentialridges 47 are provided on the upper roll 40 to provide an efficientflame snuffing action while reducing off-set problems associated withthe upper roll. A strip-type seal leaves a gap of less than about 0.030inch between the seal 61 and the hub of the roll 40 which allows aslight air flow through the sealed air channel. The amount of air flowhas been found to be very slight and not enough to cause a substantialcurl. However, it is desirable to completely seal the channel betweenthe roll 40 and the fuser 3. A brush-type seal 100 as in accordance withthe present invention performs the function of completely sealing offthe passageway since the brush fibers 102 follow the contour of the rollsurface and, therefore, fill in the valleys between the ridges 47 tosubstantially close off the air channel.

In the apparatus 1 shown, brush-type seals 100 are employed between theupper and lower transport rolls 40 and 41 on the downstream side of thefuser 3 whereas a strip type seal 64 is employed on the upstream side ofthe fuser between the fuser base 66 and the transport 20. It is apparenttherefore that it is possible in accordance with this invention toemploy seals of both the brush type 100 of this invention and the striptype 63 where desired.

The strip type seals 63 comprise an elongated strip type member formedof a resilient material which is biased against the transports 40, 4-1or 20 and extends over the respective gap between the transport and thefuser. As with the brush type seal. 100 they may be secured to the fuserby any desired means. Preferably they are formed of a polymeric materialsuch as polytetrafluoroethylene sold under the trademark Teflon andpolyethyleneterethalate sold under the trademark Mylar.

An exemplary brush 100 usable in accordance with the present inventionwhich has been employed was formed of flame proof Nomex nylon with apile yarn size of 2/10; with a plain weave for the backing; with athread count for the pile ticks of 6.25 i0.25/inch and for the pile endsof 24il/inch; with the number of tufts per square inch at 150i8% andwith a tiger texture for the brush. A brush of this type has been foundto be effective as seen from the following example.

By way of example for a fuser 3 having a gap between the platen 30 andthe reflector 32 of about /8 inch and a length normal to the plane ofH0. 3 of about inches an air flow of less than about 0.2 cfm willsubstantially reduce or eliminate curl. If the seals 61 63 are removedthe air flow through the fuser 3 shown would be about 5 cfm.

It is believed that for most radiant fusers the air flow should bemaintained below about I cfm and preferably below about 0.2 cfm in orderto reduce or eliminate curl.

The toner images of this invention may be formed from toner of the typedescribed in U.Sv Pat. Nos. 2,807,703 and 2,807,704.

The patents, applications and texts referred to specifically in thisapplication are intended to be incorporated by reference into theapplication.

It is apparent that there has been provided in accordance with thisinvention, a fusing apparatus which fully satisfies the objects, meansand advantages set forth hereinbefore. While the invention has beendescribed in conjunction with specific embodiments thereof, it isevident that many alternatives, modifications and variations will beapparent to those skilled in the art in light of the foregoingdescription. Accordingly, it is intended to embrace all suchalternatives,

modifications and variations as fall within the spirit and broad scopeof the appended claims.

What is claimed is:

1. In a fusing apparatus for heat fusing a toner image to a sheet offinal support material including:

a fuser having a source of heat radiation for application to said sheet,said fuser defining a fusing zone wherein said heat source is effectiveto fuse said image to said sheet, and a flow of air at said zone; theimprovement wherein said apparatus further includes:

means cooperating with said fuser for reducing curl of said sheet duringfusing, said curl reducing means comprising at least one seal adjacentsaid zone for limiting air flow at said zone to an amount at which curlof said sheet is substantially reduced, said seal comprising anelongated member having a brush-like configuration.

2. An apparatus as in claim I wherein said brush-like member comprises abacking strip and a plurality of elongated fibers extending out fromsaid strip in said brush-like configuration.

3. An apparatus as in claim 2 wherein said fibers are formed of apolymeric material.

4. An apparatus as in claim 3 wherein said fibers are formed of nylon.

5. An apparatus as in claim 1 further including first transport meansfor transporting said sheet, said transport means being located adjacentsaid fuser, and air channel being defined between said transport meansand said fuser, and wherein said seal extends over a gap between saidfuser and said transport means.

6. An apparatus as in claim 5 wherein said first transport means islocated at a first side of said fuser and wherein a second transportmeans is provided at the opposing side of said fuser and wherein atleast one of said first and second transport means includes suctionmeans cooperating therewith to hold said sheet to said one of saidtransport means.

7. An apparatus as in claim 6 including a plurality of said seals.

8. An apparatus as in claim 7 wherein a plurality of air channels areformed between the respective transport means and the fuser and whereinsaid seals are interposed in the channels extending over respective gapsbetween the fuser and the respective transport means.

9. An apparatus as in claim 8 wherein said first transport meanscomprises a pair of pinch rolls and wherein said second transport meanscomprises a vacuum transport having said suction means and wherein saidfirst transport is located downstream of said fuser and wherein saidsecond transport is located upstream of said fuser.

10. An apparatus as in claim 1 wherein said air flow is reduced to below1 cubic foot per minute.

1 1. An apparatus as in claim 10 wherein said air flow is reduced tobelow 0.2 cubic foot per minute.

=l l= l-' l

1. In a fusing apparatus for heat fusing a toner image to a sheet offinal support material including: a fuser having a source of heatradiation for application to said sheet, said fuser defining a fusingzone wherein said heat source is effective to fuse said image to saidsheet, and a flow of air at said zone; the improvement wherein saidapparatus further includes: means cooperating with said fuser forreducing curl of said sheet during fusing, said curl reducing meanscomprising at least one seal adjacent said zone for limiting air flow atsaid zone to an amount at which curl of said sheet is substantiallyreduced, said seal comprising an elongated member having a brush-likeconfiguration.
 2. An apparatus as in claim 1 wherein said brush-likemember comprises a backing strip and a plurality of elongated fibersextending out from said strip in said brush-like configuration.
 3. Anapparatus as in claim 2 wherein said fibers are formed of a polymericmaterial.
 4. An apparatus as in claim 3 wherein said fibers are formedof nylon.
 5. An apparatus as in claim 1 further including firsttransport means for transporting said sheet, said transport means beinglocated adjacent said fuser, and air channel being defined between saidtransport means and said fuser, and wherein said seal extends over a gapbetween said fuser and said transport means.
 6. An apparatus as in claim5 wherein said first transport means is located at a first side of saidfuser and wherein a second transport means is provided at the opposingside of said fuser and wherein at least one of said first and secondtransport means includes suction means cooperating therewith to holdsaid sheet to said one of said transport means.
 7. An apparatus as inclaim 6 including a plurality of said seals.
 8. An apparatus as in claim7 wherein a plurality of air channels are formed between the respectivetransport means and the fuser and wherein said seals are interposed inthe channels extending over respective Gaps between the fuser and therespective transport means.
 9. An apparatus as in claim 8 wherein saidfirst transport means comprises a pair of pinch rolls and wherein saidsecond transport means comprises a vacuum transport having said suctionmeans and wherein said first transport is located downstream of saidfuser and wherein said second transport is located upstream of saidfuser.
 10. An apparatus as in claim 1 wherein said air flow is reducedto below 1 cubic foot per minute.
 11. An apparatus as in claim 10wherein said air flow is reduced to below 0.2 cubic foot per minute.